Human immunodeficiency virus type 1 (HIV-1) infects the central nervous system of adults and children. Little is known about HIV-1 infection of the fetal nervous system, or about the indirect effects of maternal HIV-1 infection on the developing fetal brain. There is currently no in vitro system or related animal model available which can satisfy the chief requirements to address pathogenetic Issues or to test anti-viral agents which may treat HIV-1 brain infection. The marked host species specificity of lentiviruses and the importance of viral-host cell interactions suggest that a model is required in which intact, differentiating, human fetal neural tissue can be infected by HIV-1 and/or exposed to potentially toxic viral or host derived factors. We have developed a model in which human second trimester fetal brain or retinal tissues are grown as xenografts in the anterior chamber of the eye in adult rats. These xenografts vascularize, establish a blood-brain-barrier, and differentiate into astroglial, microglial, and neuronal elements. We propose to establish and optimize conditions for infecting these human fetal neural tissues with HIV-1. Experiments are proposed employing cell free virus, virus infected lymphocytes and macrophages, and fetal neural explants infected in vitro prior to transplantation (Specific Aim 1). To determine the cellular localization and to analyze the course of the HIV-1 infection in these xenografts, we will use polymerase chain reaction (PCR), coupled with immunohistochemical and in situ hybridization techniques. This will identify which cell types (neuroectodermal or other) are infected, and the nature of Infection in each cell type (productive, restricted, or latent). Complementary studies will be performed using in vitro methods to segregate neuronal, astroglial, and microglial components, followed by re-aggregation of specific combinations of these cells, in the xenograft, to serve as a target for HIV-1 infection. (Specific Aim 2) We will evaluate the feasibility of of using this model to assess the efficacy and toxicity of antiviral agents which target HIV-1 infection of the nervous system (Specific Aim 3). Lastly we will use the xenograft model to determine the indirect effects on the developing nervous system of putative toxic factors of host cell or viral origin (Specific Aim 4).